Method and apparatus for starting detonation combustion engines

ABSTRACT

1. In a method of starting a detonation combustion engine having an aerothermodynamic duct which includes an adjustable inlet and an adjustable throat adjacent the combustion zone and is adapted to receive a hypersonic stream of air during normal operation, the steps comprising reducing the amount of air supplied by the inlet to the throat while simultaneously opening the throat until at least sonic velocity of the fluid stream is attained at the combustion zone, then gradually increasing the amount of air supplied by the inlet to the throat, feeding fuel into the fluid stream, and restricting the throat so as to adjust the flow to obtain the desired velocity, temperature and pressure for detonation in said combustion zone.

United States Patent Norman et al.

[ Mar. 7, 1972 [72] Inventors: Leslie W. Norman, Scottsdale; Skillman C.Hunter; George L. Perrone, both of Phoenix, all of Ariz.

[73] Assignee: The Garrett Corporation, Los Angeles,

Calif.

[22] Filed: Mar.7,1961

[2]] Appl. No.: 94,022

OTHER PUBLICATIONS Cushman Scientists Study Mach 7 Ramjet Theory,"Aviation Week, Vol. 68, No. 1, Jan. 6, 1958- pages 57 59 and 63 PrimaryExaminer-Robert F. Stahl Attorney-Herschel C. Omohundro and John H. G.Wallace EXEMPLARY CLAIM 1. In a method of starting a detonationcombustion engine having an aerothennodynamic duct which includes anadjustable inlet and an adjustable throat adjacent the combustion zoneand is adapted to receive a hypersonic stream of air during normaloperation, the steps comprising reducing the amount of air supplied bythe inlet to the throat while simultaneously opening the throat until atleast sonic velocity of the fluid stream is attained at the combustionzone, then gradually increasing the amount of air supplied by the inletto the throat, feeding fuel into the fluid stream, and restricting thethroat so as to adjust the flow to obtain the desired velocity,temperature and pressure for detonation in said combustion zone.

8 Claims, 7 Drawing Figures 0000 0 0 0. .0. 0000 0.000 0 00 0 m mw 000060 0 0000 0000 0 00 0 00 0 mmw 0000 00 0 000. 0000 0000 0 0 02 t R R.0025 0000 00 0 0.00. 00000 0 b0. 0 0 000 00 0 00: 0000; 0 00. 0 mmw M0000 2 0 0. .0 0000 0 00. 0 MM W 0 000 00 0 05 003 0 00 0. 5 0% x 02.000 0 000 h 0000 0 0.2 0. J 0 000 00 0 000. 0000 .000 0 0 \A 9 6%: E: E0E0 020: 2.0% OU 0 0 W 0. 0 0% 00 000 5 2%: ML.

PATENTEUMAR 7 I972 A TTORNE'Y METHOD AND APPARATUS FOR STARTINGDETONATION COMBUSTION ENGINES This inventionrelates to airbreathingengines for aircraft, and aims to provide a method of and means forcontrolling the intake and airflow during the starting of a detonationcombustion engine used in hypersonic aircraft.

In the copending application of Hunter and Norman, Ser. No. 88,149 filedFeb. 9, 1961, a detonation combustion engine is disclosed which isdesigned specifically for :use in hypersonic aircraft. Accordingto theHunter and Norman application, the flame front or detonation isestablished and maintained by positioning and maintaining a stableaerodynamic shock system in a variable geometry aerothermodynamic ductorengine such that the-heat release occurs across a shock wave, ratherthan being maintained by a flame holder as is the case in conventionalinternal combustion processes such as occur in ramjet and turbojetengines. Steady state detonation is established and maintained across astanding shock wave of fixed position relative-to a confining structuretherefor, and subsequent expansion of the gaseous detonation product isused to develop a continuous thrust.

Starting the detonation combustion process in a detonation combustionengine having an aerothermodynamic duct presents many of the sameproblems that are encountered in wind tunnels and supersonic inlets.Immediately upon opening the duct or engine inlet to a hypersonic (Machnumber above 5.0) free stream, the conditions inside the duct, beingsubsonic, are such that the air captured by the inlet cannot becompletely passed through it. As a result, a detached normal shock waveforms outside the inlet lip in such a position as to allow sutficientair to spill out the sides that the remainder passes through the duct ata subsonic rate which is thus inadequate for the production of thedesired conditions for detonation combustion.

The present invention is based on the discovery that in a variablegeometry detonation combustion engine, the abovementioned startingdifficulties may be-completely eliminated by diverting a sufficientportion of the inlet air, while at the same time opening the throatimmediately adjacent the detonation combustion zone, that the capturedair may proceed through the engine to the detonation combustion zone atthe desired supersonic velocity. When this result is attained, theamount of air allowed into the engine atthe inlet may be increased tothe full stream striking the inlet, and subsequently the throatimmediately adjacent the zone of detonation may be restricted so as toadjust the levels of pressure, temperature and velocity to the operatingcondition most favorable for detonation with minimum specific fuelconsumption for the thrust required.

It is therefore an object of this invention to provide an efficientmethod of and means for starting a detonation combustion engine designedfor use in hypersonic aircraft.

Another object of this invention is to provide an efficient method ofstarting a variable geometry detonation combustion engine in which theamount of air entering the engine and the rate of flow through theengine are adjusted to effect ideal conditions for detonation.

A further object of this invention is to provide a method of starting adetonation combustion engine having an adjustable inlet and anadjustable throat adjacent the combustion zone, which method comprisesreducing the amount of air entering the inlet while simultaneouslyopening the throat until a predetermined velocity of the fluid stream isattained at the combustion zone, then gradually increasing the amount ofair entering the inlet and reducing the throat area to obtain thedesired velocity, temperature and pressure for detonation in saidcombustion zone when a suitable fuel is injected into the fluid stream.

The above and other objects of the invention will be apparent from thefollowing description and the accompanying drawing, in which:

FIG. I is a schematic side elevational view of a hypersonic aircrafthaving a detonation combustion engine embodying the principles of theinvention;

FIG. 2 is a schematic plan view of the detonation combustion engineshown in FIG. 1;

FIG. 3 is a table of the values of pressure, temperature,

-Mach number, and velocity prevailing in the various flow repersonicpropagation velocity and a large pressure and temperatureincrease acrossthe wave. A detonation differs from a subsonic flame in that such aflame moves with subsonic velocity andits microscopic propagationmechanisms are fundamentally different. The supersonic combustion waveproduces strong detonation which is stable, steady, reproducible, andobtainable over a wide fuel-air-ratio as long as the Mach number of theapproach flow is'greater than the Chapman-Jouguet Mach number for thatfuel-air ratio. A Chapman-Jouguet" detonation is characterized by thefact that the flow immediately behind the wave is sonic, i.e., a Machnumber of one, and such a detonation represents the minimum supersonicpropagation Mach number for a given fuel-air ratio.

Experiment has shown that detonation combustion takes place under thefollowing conditions:

I. A stream of gases is moving supersonically relative to thecontainment vessel or aerothermodynamic duct;

2. The total temperature of the supersonic gas stream must exceed thedetonation temperature of the gas stream;

3. The gas stream consists of a mixture of some oxidizer, such as air,and unburned fuel; such as hydrogen; and

4. A shock system of such strength is generated at some point in theaerothermodynamic duct that the static temperature across the shocksystem is high enough to cause detonation.

This type of detonation can occur across a normal shock wave whence theMach number downstream of the shock wave will be subsonic. The samephenomena may occur across an oblique shock wave as long as the statictemperature downstream of the shock wave is sufficiently high to causedetonation.

Referring now to FIGS. 1 and 2, a hypersonic aircraft A, shownschematically, is powered by a variable geometry detonation combustionengine E to' produce hypersonic speeds in the range of 6 to 7 Machnumber at an altitude of 125,000 feet. The design of the airframe andthe inlet of the engine are such as to produce a series of shock wave8,, S S S S and S which will slow the captured flow from a free streamMach number of 6.5 to a Mach number of 2.5 at the inlet to thedetonation zone. The manner of producing the shock waves to accomplishthis reduction in Mach number, with an attendant increase in staticpressure and static temperature, is fully described in the copendingHunter and Norman application referred to above. Briefly, the design ofthe airframe is such that first and second critical shock waves S and S:are produced upstream of the inlet to the engine E. These waves defineregions 12 and 13 wherein the pressure, temperature, velocity, and Machnumbers have the values shown in the table of FIG. 3. Region 11 is thefree stream adjacent the aircraft. The geometry of the engine is suchthat shock waves 8;, and S are formed and create regions 14, I5 and 16where the physical conditions are as tabulated in FIG. 3. Next, criticalshock wave S (FIG. 1) is created by the hinged leading edge of anadjustable ramp or door 20 which is arranged in the combustion zoneimmediately upstream from the normal shock wave 5,. This last wave S, isthe one across which detonation combustion takes place. Wave S, createszone 17, immediately prior to combustion, and the physical conditions inthis zone are at least partially controlled by the angle of theadjustable ramp, as will be described more fully hereinafter.

The table of FIG. 3 shows that a stepwise increase in static temperatureaccompanies each successive shock wave in the aircraft and engine ductsystem. To take advantage of this increase, a fuel, such as hydrogen,having a detonation temperature below the static temperature occurringin the normal shock wave S, is recommended. The FIG. 3 table alsoindicates that the statictemperature occurring in the flow region 17downstream of oblique shock wave 8,, may be higher than the temperaturerequired for initiation of combustion in the air-hydrogen mixture. Thetime required for this mixture to traverse region 17 is so short,however, in comparison to the time needed to achieve combustion, thatthe mixture may remain chemically unafl'ected until it reaches thenormal shock wave 8,. Here (region 18) the static temperature rises withconsequent detonation of the mixture and a further increase in statictemperature to 4,950R., as shown in FIG. 3 Finally, region 19, at therear of the exhaust, indicates the con- .ditions of thrust.

The foregoing explanation of the shock wave system pertains primarily tothe operation of the engine during cruising. As explained in the Hunterand Norman application above referred to, the aircraft may beaccelerated to a hypersonic cruising speed of about Mach number 6.5, forexample, by a jettisonable booster rocket (not shown). During thisinitial period of acceleration, the inlet 21 of engine E is closed by aremovable door 22 which also may be jettisoned when it is desired tostart the engine in accordance with the principles of this invention.

Assuming now that the aircraft has been accelerated to the desiredcruising speed and the removable door has been jettisoned, at thismoment, the air inside the aerothermodynamic duct of the engine will besubstantially stationary or subsonic. When the full force of theairstream then strikes the inlet 21, the air captured by the inletcannot be completely passed through it because the air in the duct issubsonic. As a result, a normal shock wave 5, forms outside the inletlip, as indicated in FIG. 4, in such a position as to allow largeamounts of air to spill out the sides of the inlet 21. It has been foundthat the amount spilled is such that the remainder then passes throughthe engine duct at a subsonic rate which is thus inadequate for theproduction of the desired conditions for detonation combustion.

To eliminate this difficulty and permit the development of the desiredsupersonic velocities in the engine duct, as described above andindicated in the table of FIG. 3, the procedure now to be described andforming the subject matter of this invention is followed. In FIGS. 1 and4-7, it will be noted that a special movable door'23 is provided in thelower wall or floor of engine E near or immediately downstream of theinlet 21. This door 23 is normally flush with the bottom of the duct andfunctions in cooperation with the adjustable ramp 20 during the startingoperation.

As shown in FIG. 4, when the removable cover 22 is jettisoned, the door23 is closed and the ramp 20 is moved to the open position shown by anyconventional means, such as a pneumatic piston 24 which is arranged toreceive fluid pressure from a suitable source 25. When the ramp 20 is inthis open position, the throat of the engine duct immediately adjacentthe combustion zone is wide open and substantially unrestricted. Inspike of this, however, the normal shock wave 8,, will stay outside theinlet if the doors 23 and 20 remain in the FIG. 4 position. According tothis invention, part of the captured air is bypassed by opening theinlet door 23 to the FIG. position, and this permits the normal shockwave 8,, to move downstream past the inlet lip as indicated. Inlet door23 may be moved to open position in any desired manner, such as by asecond pneumatic piston 26 also supplied with fluid under pressure fromsource 25.

Having thus moved inside the inlet, the normal shock wave S, proceeds ondownstream, with the establishment of suitable operating conditions,until it reaches the position shown in FIG. 1 where it is retained bysteep angled wedges 27 (FIG. 2). This is the position in whichdetonation combustion takes place following the injection ofpredetermined amounts of fuel, such as hydrogen. The fuel may be fedfrom a supply tank 28 to a plurality of injectors 30 which arepositioned in the engine duct upstream of the combustion zone, such asin region 14. Prior to the injection of fuel, however, the amount ofbypassed air is decreased by closing the door 23 gradually (FIG. 6); andsubstantially at the same time adjusting the angle of the combustor rampupwardly to some position between those shown in FIGS. 6 and 7,depending upon the specific conditions desired. The adjustability of theangle of the ramp 20 makes it possible to regulate the velocity,temperature and pressure to those suitable for detonation, so that whenfuel is then added, as described above, such detonation will take placeat the FIG. 1 position of wave 8,. When the ramp 20 is in its fully openposition, rendering the throat adjacent the combustion zonesubstantially unrestricted, the contraction ratio of the engine duct isdecreased, resulting in the required reduction of the amount of bypassedair to effect the desired downstream movement of the normal shock waveS3.

Various changes may be made in the method and means described herein,and certain features may be employed without others, without departingfrom this invention or sacrificing any of its advantages.

We claim:

1. In a method of starting a detonation combustion engine having anaerothermodynamic duct which includes an adjustable inlet and anadjustable throat adjacent the combustion zone and is adapted to receivea hypersonic stream of air during normal operation, the steps comprisingreducing the amount of air supplied by the inlet to the throat whilesimultaneously opening the throat until at least sonic velocity of thefluid stream is attained at the combustion zone, then graduallyincreasing the amount of air supplied by the inlet to the throat,feeding fuel into the fluid stream, and restricting the throat so as toadjust the flow to obtain the desired velocity, temperature and pressurefor detonation in said combustion zone.

2. A method of starting a detonation combustion engine having anaerothermodynamic duct which includes an adjustable inlet and anadjustable throat adjacent the combustion zone and is adapted toreceivea hypersonic stream of air during normal operation, which methodcomprises reducing the amount of air supplied by the inlet to the throatwhile simultaneously opening the throat until at least sonic velocity ofthe fluid stream is attained at the combustion zone, graduallyincreasing the amount of air supplied by the inlet to the throat andflowing to the combustion zone at such velocity, feeding fuel into suchairstream, and restricting the throat adjacent the combustion zone toadjust the velocity, temperature and pressure to the predeterminedvalues required for minimum specific fuel consumption.

3. In a method of starting a detonation combustion engine having anaerothermodynamic duct which includes an adjustable inlet door and anadjustable throat adjacent the combustion zone, and in which as the freeairstream strikes the inlet a detached normal shock wave is formedoutside said inlet, the steps comprising bypassing a portion of thecaptured air by opening said adjustable inlet door while regulating saidadjustable throat to a substantially completely open position so thatsaid normal shock wave will be caused to move through said inlet anddownstream in the duct to the combustion zone, and then closing saidadjustable inlet door, feeding fuel into said duct, and regulating saidadjustable throat to adjust the thermodynamic conditions to those atwhich detonation will take place.

4. A method of starting a detonation combustion engine having anaerothermodynamic duct which includes an adjustable inlet door and anadjustable throat adjacent the combustion zone, and in which as the freeairstream strikes the inlet a detached normal shock wave is formedoutside said inlet, which method comprises bypassing a portion of thecap tured air by opening said adjustable inlet door while regulatingsaid adjustable throat to a substantially completely open position sothat said normal shock wave will be caused to move through said inletand downstream in the duct to the combustion zone, and then closing saidadjustable inlet door, feeding fuel into the air stream flowing throughthe duct, and regulating said adjustable throat so as to adjust theaerothermodynamic conditions in the combustion zone to those at whichdetonation will take place.

5. A detonation combustion engine comprising: an aerothermodynamic ducthaving an inlet, a mixing section, a combustion zone having a throatadjacent thereto, and an exhaust nozzle; a door in said duct adjacentsaid inlet, said door being adjustable between an open position todivert air from said duct to the exterior and a closed position in whichno air is diverted; an adjustable ramp immediately upstream of saidcombustion zone and movable between an open position substantially flushwith a wall of the duct and an angular position which reduces the areaof the throat adjacent said combustion zone; means for opening said doorand moving said ramp to open position during the starting of thedetonation combustion engine; and means for feeding fuel into saidmixing section.

6. A detonation combustion engine comprising: an aerothermodynamic ducthaving an inlet, a mixing section, a combustion zone with a throatadjacent thereto, and an exhaust nonle; an adjustable door in said ductadjacent said inlet and movable between a closed position substantiallyflush with a wall of said duct and an open position which permits partof an incoming airstream to be bypassed; means for injecting fuel intothe mixing section of said duct; an adjustable ramp immediately upstreamof said combustion zone and movable between an open positionsubstantially flush with a wall of the duct and an angular positionwhich reduces the area of the throat adjacent said combustion zone; andmeans for opening said door and moving said ramp to open position duringthe starting of the detonation combustion engine.

7. A method of starting a detonation combustion engine having anaerothermodynamic duct which includes an adjustable inlet and anadjustable throat adjacent the combustion zone and is adapted to receivea hypersonic stream of air during normal operation, which methodcomprises reducing the amount of air supplied by the inlet to the throatwhile simultaneously adjusting the throat until a velocity of the fluidstream sufficient to produce a shock wave is attained at the combustionzone, then gradually increasing the amount of air supplied by the inletto the throat, feeding fuel into the fluid stream, and adjusting theflow conditions in said duct by the regulation of the adjustable throatto obtain the desired velocity, temperature and pressure for detonationin said combustion zone.

8. A detonation combustion engine comprising: an aerothermodynamic ducthaving an inlet, a mixing section, a combustion zone having a throatadjacent thereto, and an exhaust nozzle; adjustable means adjacent theinlet for changing the amount of air supplied by the inlet to thethroat; ramp means upstream of the combustion zone, said ramp meansbeing movable independently of the adjustable means adjacent said inletto change the area of the throat; means for feeding fuel into said duct;means for moving said adjustable means to reduce the amount of airsupplied by the inlet to the throat; and means for moving said rampmeans to increase the area of said throat during the starting of thedetonation combustion engine.

1. In a method of starting a detonation combustion engine having anaerothermodynamic duct which includes an adjustable inlet and anadjustable throat adjacent the combustion zone and is adapted to receivea hypersonic stream of air during normal operation, the steps comprisingreducing the amount of air supplied by the inlet to the throat whilesimultaneously opening the thRoat until at least sonic velocity of thefluid stream is attained at the combustion zone, then graduallyincreasing the amount of air supplied by the inlet to the throat,feeding fuel into the fluid stream, and restricting the throat so as toadjust the flow to obtain the desired velocity, temperature and pressurefor detonation in said combustion zone.
 2. A method of starting adetonation combustion engine having an aerothermodynamic duct whichincludes an adjustable inlet and an adjustable throat adjacent thecombustion zone and is adapted to receive a hypersonic stream of airduring normal operation, which method comprises reducing the amount ofair supplied by the inlet to the throat while simultaneously opening thethroat until at least sonic velocity of the fluid stream is attained atthe combustion zone, gradually increasing the amount of air supplied bythe inlet to the throat and flowing to the combustion zone at suchvelocity, feeding fuel into such airstream, and restricting the throatadjacent the combustion zone to adjust the velocity, temperature andpressure to the predetermined values required for minimum specific fuelconsumption.
 3. In a method of starting a detonation combustion enginehaving an aerothermodynamic duct which includes an adjustable inlet doorand an adjustable throat adjacent the combustion zone, and in which asthe free airstream strikes the inlet a detached normal shock wave isformed outside said inlet, the steps comprising bypassing a portion ofthe captured air by opening said adjustable inlet door while regulatingsaid adjustable throat to a substantially completely open position sothat said normal shock wave will be caused to move through said inletand downstream in the duct to the combustion zone, and then closing saidadjustable inlet door, feeding fuel into said duct, and regulating saidadjustable throat to adjust the thermodynamic conditions to those atwhich detonation will take place.
 4. A method of starting a detonationcombustion engine having an aerothermodynamic duct which includes anadjustable inlet door and an adjustable throat adjacent the combustionzone, and in which as the free airstream strikes the inlet a detachednormal shock wave is formed outside said inlet, which method comprisesbypassing a portion of the captured air by opening said adjustable inletdoor while regulating said adjustable throat to a substantiallycompletely open position so that said normal shock wave will be causedto move through said inlet and downstream in the duct to the combustionzone, and then closing said adjustable inlet door, feeding fuel into theair stream flowing through the duct, and regulating said adjustablethroat so as to adjust the aerothermodynamic conditions in thecombustion zone to those at which detonation will take place.
 5. Adetonation combustion engine comprising: an aerothermodynamic ducthaving an inlet, a mixing section, a combustion zone having a throatadjacent thereto, and an exhaust nozzle; a door in said duct adjacentsaid inlet, said door being adjustable between an open position todivert air from said duct to the exterior and a closed position in whichno air is diverted; an adjustable ramp immediately upstream of saidcombustion zone and movable between an open position substantially flushwith a wall of the duct and an angular position which reduces the areaof the throat adjacent said combustion zone; means for opening said doorand moving said ramp to open position during the starting of thedetonation combustion engine; and means for feeding fuel into saidmixing section.
 6. A detonation combustion engine comprising: anaerothermodynamic duct having an inlet, a mixing section, a combustionzone with a throat adjacent thereto, and an exhaust nozzle; anadjustable door in said duct adjacent said inlet and movable between aclosed position substantially flush with a wall of said duct and an openposition which permits part of an incoming airstream to be bypassed;means for injecting fuel intO the mixing section of said duct; anadjustable ramp immediately upstream of said combustion zone and movablebetween an open position substantially flush with a wall of the duct andan angular position which reduces the area of the throat adjacent saidcombustion zone; and means for opening said door and moving said ramp toopen position during the starting of the detonation combustion engine.7. A method of starting a detonation combustion engine having anaerothermodynamic duct which includes an adjustable inlet and anadjustable throat adjacent the combustion zone and is adapted to receivea hypersonic stream of air during normal operation, which methodcomprises reducing the amount of air supplied by the inlet to the throatwhile simultaneously adjusting the throat until a velocity of the fluidstream sufficient to produce a shock wave is attained at the combustionzone, then gradually increasing the amount of air supplied by the inletto the throat, feeding fuel into the fluid stream, and adjusting theflow conditions in said duct by the regulation of the adjustable throatto obtain the desired velocity, temperature and pressure for detonationin said combustion zone.
 8. A detonation combustion engine comprising:an aerothermodynamic duct having an inlet, a mixing section, acombustion zone having a throat adjacent thereto, and an exhaust nozzle;adjustable means adjacent the inlet for changing the amount of airsupplied by the inlet to the throat; ramp means upstream of thecombustion zone, said ramp means being movable independently of theadjustable means adjacent said inlet to change the area of the throat;means for feeding fuel into said duct; means for moving said adjustablemeans to reduce the amount of air supplied by the inlet to the throat;and means for moving said ramp means to increase the area of said throatduring the starting of the detonation combustion engine.